arch/x86: print cr2 value on every exception

Even though most x86 systems don't run with paging on, it's
helpful to always print it out for the ones that do without
making a more complicated handler. New dump will look like
the following:

Unexpected Exception: 6 @ 10:7ab84be2 - Halting
Code: 0 eflags: 00010006 cr2: 00000000
eax: 7abb80ec ebx: deadbeef ecx: 00000000 edx: 00000002
edi: 7abb3000 esi: 00000004 ebp: 7abb2fd8 esp: 7abb2fb0

7ab84ba0:       00 01 00 83 ec 0c 6a 39
7ab84ba8:       e8 8a 02 01 00 e8 e1 08
7ab84bb0:       00 00 e8 4e 3d 00 00 59
7ab84bb8:       5b 52 50 e8 f5 3c 00 00
7ab84bc0:       c7 04 24 0a 00 00 00 e8
7ab84bc8:       3c 3d 00 00 c7 04 24 80
7ab84bd0:       00 00 00 e8 5f 02 01 00
7ab84bd8:       e8 1e 38 01 00 e8 7e 50
7ab84be0:       01 00 0f 0b bb 98 ec ba
7ab84be8:       7a 83 c4 10 8b 03 85 c0
7ab84bf0:       0f 84 be 00 00 00 83 78
7ab84bf8:       04 00 8d 50 08 75 0c 56
7ab84c00:       56 ff 30 52 e8 f8 fe ff
7ab84c08:       ff eb 0a 51 51 ff 30 52
7ab84c10:       e8 2e ff ff ff 83 c4 10
7ab84c18:       83 c3 04 eb cf 89 d8 e8

BUG=b:72728953

Change-Id: I0e87bbe776f77623ad8297f5d80167998daec6ed
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/25762
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/arch/x86/exception.c

@@ -17,6 +17,7 @@
 #include <compiler.h>
 #include <console/console.h>
 #include <console/streams.h>
+#include <cpu/x86/cr.h>
 #include <rules.h>
 #include <stdint.h>
 #include <string.h>
@@ -503,11 +504,11 @@ void x86_exception(struct eregs *info)
 #define MDUMP_SIZE 0x80
 	printk(BIOS_EMERG,
 		"Unexpected Exception: %d @ %02x:%08x - Halting\n"
-		"Code: %d eflags: %08x\n"
+		"Code: %d eflags: %08x cr2: %08x\n"
 		"eax: %08x ebx: %08x ecx: %08x edx: %08x\n"
 		"edi: %08x esi: %08x ebp: %08x esp: %08x\n",
 		info->vector, info->cs, info->eip,
-		info->error_code, info->eflags,
+		info->error_code, info->eflags, read_cr2(),
 		info->eax, info->ebx, info->ecx, info->edx,
 		info->edi, info->esi, info->ebp, info->esp);
 	u8 *code = (u8 *)((uintptr_t)info->eip - (MDUMP_SIZE >> 1));

src/include/cpu/x86/cr.h

@@ -59,6 +59,18 @@ static alwaysinline void write_cr0(CRx_TYPE data)
 	);
 }
 
+static alwaysinline CRx_TYPE read_cr2(void)
+{
+	CRx_TYPE value;
+	__asm__ __volatile__ (
+		"mov %%cr2, %0"
+		: CRx_RET(value)
+		:
+		: COMPILER_BARRIER
+	);
+	return value;
+}
+
 static alwaysinline CRx_TYPE read_cr3(void)
 {
 	CRx_TYPE value;